Copying process



Patented Sept. 26, 1944 COPYING PROCESS George W. Jorgensen, Chicago, Ill., assignor of five per cent to Harriette Moore, Chicago, Ill.

No Drawing. Application December 22, 1941, Serial No. 424,055

3 Claims.

Processes for preparing copies of printed matter involving the use of light reflection, as now practiced, comprise placing a silver halide emulsion in contact with the paper to be copied, with the emulsion side in contact with the printed surface. Light from a suitable light source is then allowed to pass through the emulsion to the material to be copied, so that where there is a medium or deposit such as ink present, the light is absorbed and stopped, and the light is reflected back through the emulsion on the clear areas, so that the same is exposed to the light so that a negative copy of the original on the emulsion is obtained when the emulsion is developed. This negative is then printed on blueprint or photographic paper. The foregoing processes, well known in the art, have several drawbacks, such as that the crystalline character of the halides scatter the light and thereby lower the clarity and definition of the copy, the emulsions and materials used are expensive, and it is necessary to keep the temperature of the solutions within a narrow range (65 to '70 degrees F.); and three chemical solutions are needed in the development of the emulsion which is required to be processed in a dark room.

In order to overcome the foregoing drawbacks and difficulties, I have evolved a process which while retaining the basic advantages of the former processes referred to, eliminates the above mentioned disadvantages while procuring other advantages, such as that copies of the printed matter or the like can be made without the grain in the paper in the original showing, the copies made are exact in detail and size compared with the original, so that the errors of hand tracing and the slowness thereof are eliminated, and the material used as the light sensitive emulsion is a clear transparent gelatin with a slight yellow tint from the chromate that is used in lighttanning and has a high contrast range. Further, there is no need for a dark room in operating the process and all the steps of the process can be carried on under subdued light. The emulsion and the developing solution can be easily prepared by the operator and the component materials are not expensive. The only apparatus and equipment needed are, a tray large enough for the emulsion and the developer, and an actinic light source.

In eliminating the foregoing disadvantages and obtaining the advantages and others set forth, I expressly do not limit myself to the examples and embodiments of the invention which are set forth herein below for illustrative pur-,

poses.

Equipment Gelatin grams 250 Sodium stearate do 25 40% formaldehyde solution ml 003 Or phenol gram 001 Water to make -liter 001 The formaldehyde or phenol acts as a preservative for the gelatin. When the coating is to be put on glass plates, the sodium stearate may be left out since it is used to give pliancy to the emulsion when coated on plastics. Before coating, ml. of ethyl alcohol is added to prevent bubbles in the emulsion, and to speed its setting. The gelatin should be a medium soft type with a melting point of about F. The gelatin is first soaked in cold water and then melted at a higher temperature, the stearate is then added and the volume diluted to 1 liter. After the emulsion has been coated and set, it may be stored until needed.

The sensitizing solution-The above emulsion not being light sensitive, some agent must be added that will make the emulsion show a physical difference when it is exposed to strong light, such as the chromate ion which has the property of tanning gelatin in direct proportion to the amount of light that hits it. The exact manner in which this reaction takes place is not known, but what apparently happens is that the hexa-valent chromium ion, Cr in the presence of organic matter is reduced by the action of light to the chromium ion, Cr with a valence of three. This chromium ion with a valence of three can unite with gelatin to form a gelatinate, since gelatin is a polypeptide and can act as a base or acid. Since the metal gelatinates have a much higher melting point than pure gelatin, there will be a physical difference in that part of the emulsion that has been exposed to light. This reaction is used in carbon printing, one of the oldest photography printin methods, and I have found that it can be applied to reflection printing with some modifications. Unlike carbon printing, no pigment is here present to decrease the amount of light that passes through the emulsion, and the concentration of the chromate ion is reduced in order'to have a high contrast range. Although the dichromate ion is used in preparing the sensitizing solution, it is the chromate ion that is used in light-tanning since the high concentration of the hydroxide ion favors the formation of the chromate ion:

Ammonium hydroxide is added to the solution to supply the hydroxide ions. The reasons for using the chromate ion are, its yellow color which allows more light to pass through the emulsion than the dichromate ion which is deep red, and the tanning of the gelatin is faster in an alkaline condition than in an acid condition. (The dichromate ion is acid.) The iso-electric point of gelatin is in the range of a pH of 4.6 so that any solution with a pH greater than 4.6 (more alkaline) will promote the acid groups in the gelatin and thus favor the formation of the metal gelatinates (by tanning action). The formation of the gelatinates proceeds faster in an alkaline solution thereby reducing the required exposure time. A suitable sensitizing formula is:

Ammonium dichromate gram 40 Water to make liter 01 Wetting agent gram 01 The above solution is titrated with ammonium hydroxide to the appearance of a pale yellow color. The wetting agents that are suitable are Naccanol or Gardinal WA. Before use, two parts of the prepared solution are added to one part of ethyl alcohol. However, the alcohol may be substituted by acetone or water since it is present only to speed the drying of the emulsion. This solution must be discarded after use because over a period of time the alcohol will be oxidized by the chromate. To sensitize the emulsion, it is placed in a tray and the chromatoalcohol solution poured over it. At a temperature of 60 F. the time of sensitization is four minutes. It is then removed from the tray solution and placed in a current of air to dry. Since it is now sensitized to light it should not be exposed to too strong direct light, but it can be placed in dim light without harm. As soon as it is free from tackiness it is ready to be exposed, the drying time being about five minutes.

Process of copying To make the exposure the emulsion side of the support is placed in contact with the original to be copied and the exposure is made through the support. A photographic printing frame or a blueprint machine can be used to get better contact between the emulsion and the original to be copied. The exposure is made with an actinic source. The exposure is checked by the appearance of a brown image in the clear areas over the original which will appear in about 50 seconds, the time varying somewhat in accordance with the power of the light source, its distance away, and the color of the paper in the original. When the brown image appears, the light source is turned off, and the emulsion removed from the original, and is then ready for developing.

The developer and developing operation As a result of the foregoing operations, there is a weak image of the original on the emulsion in the form of a brown stain which must be intensified before it can be used for printing copies. This image is brought out and intensified by removing that part of the gelatin that was in contact with the ink of the original. The gelatin that remains in place is then dyed a deep color. It will be understood that the gelatin in that part of the emulsion that was in contact with the ink received less exposure because the ink absorbed the light from the light source, while the clear areas of the copied original reflected the light back through the emulsion and thereby increased the tanning action in that area. As a result the melting point of the clear area of the emulsion is higher than that of the inked area, due to the greater tanning action. Thus when the emulsion at this stage is placed in a tray of hot water which is at a temperature above the melting point of the inked area gelatin, but below the melting point of the clear area gelatin, the inked area gelatin will wash oif and leave the clear area gelatin. This gelatin is then dyed to a suitable color. Experiment shows that there are two image layers formed. When the emulsion is first placed in water, the areas corresponding to the inked portions are swollen into a high relief. As the temperature of the solution is raised, these raised areas dissolve away leaving the first or primary image. However, if the temperature is raised still higher, part of the remaining first or primary image is washed away, revealing below it a second or secondary image layer. This secondary image is much more firm and strong than the primary and is more suitable for use in the process.

The wash-off action and the dye action can be combined in one solution instead of the expected two different solutions. This not only dispenses with multiple solutions but also as a control for the operator since the sensitized emulsion being very transparent it is diflicult to tell when the inked area has washed off, but this difiiculty is eliminated if the emulsion is dyed a dark color as the untanned areas are washed clear. To produce this desirable effect the developer solution is prepared at a temperature below the melting point of the inked area F.) and the emulsion placed in it. When the emulsion has been dyed deeply enough to be seen, the temperature of the solution is elevated by adding water at a higher temperature until the under exposed areas wash clear. The emulsion, which is now the negative of the original may be placed in a bath of alcohol to dehydrate the gelatin, the operation consuming about three minutes. The dehydrated gelatin is then removed from the alcohol, any drops of the solution are wiped off. The negative is now ready to be printed on photographic or blue-print paper, to produce a positive copy.

The single solution mentioned which takes-the place of the expected two different solutions, for washing and dyeing of the gelatin consists preferably of the following ingredients:

Dye grams 3 to 15 7 Water (90 F.) to make liter 01 Wetting agent gram 01 The concentration of the dyes in the foregoing formula will vary because of their solubilities. However, in general the 'acid dyes will require about 3 to 5 grams plus a small amount of acetic acid, while the direct dyes, such as household dyes, will need about 8 to grams. The main requirements for a proyer dye are that it absorb and screen out all the blue light, since it is the blue light to which the blue-print paper is sensitive, and that the dye stain the gelatin rapidly. Among the colors which are suitable are black, red, green, orange and deep yellow.

After the emulsion has been in the dyeing and washing solution above described for about three to four minutes, hot water at a temperature of about 140 F. is added slowly tothe solution and the emulsion checked until the non-image areas begin to wash out to reveal a primary image layer and as the temperature is increased a lower or secondary image layer is revealed, whereat the addition of hot water is stopped. The emulsion is then allowed to remain for about 6 to 7 minutes longer in the diluted solution to absorb the dye deeply. As a substitute for the alcohol bath, a saturated solution of potassium carbonate can be used to dehydrate the gelatin.

In conclusion, it will be apparent that the time necessary to complete the process produc ing a blueprint totals from to minutes, involving as it does a flve minute period to sensitize the emulsion, a period of from 5 to 8 minutes to dry in the air, about 2 minutes to prepare and expose the emulsion and original, 15 to 20 minutes to develop and dye the negative, and 3 minutes in the alcohol bath. If ready prepared emulsion is used the total time can be reduced to less than 20 minutes.

Although I have shown and described herein preferred embodiments of my invention, it is to be definitely understood that I do not wish to limit the application of my invention thereto, except as may be required by the scope of the subjoined claims.

Having described the invention, what is claiine as new is:

1. A process of the character described consisting in supporting an unsensitized gelatin emulsion on a transparent medium, then sensitizing said gelatin emulsion with an alkaline chromate solution whereby difierent degrees of light intensity will eifect corresponding degrees of tanning of the emulsion, then drying the sensitized emulsion and placing the dried emulsion in direct contact with the surface of the printed matter or the like to be copied, then exposing the emulsion remote from the light source, then developing the exposed emulsion, by washing oil the less tanned areas of the emulsion till the first image appears, then raising the temperature of the developing bath until this image layer is washed away revealing a second image directly below it in the emulsion, then drying the remaining secondary image layer corresponding to the printed areas of the printed matter.

2. A process of the character described in claim 1 in which said gelatin emulsion consists of approximate proportions of 250 grams gelatin, 25 grams sodium stearate, 3 milliliters of 40% formaldehyde solution, and 1 liter of water; said sensitizing means consisting of about 40 grams ammoniumdichromate, and 1 gram of a wetting agent and one liter of water and sufllcient ammonium hydroxide to change the solution to a light yellow color.

3. A process of the character described in claim 1 in which said gelatin emulsion consists of approximate proportions of 250 grams gelatin, 25 grams sodium stearate, 3 milliliters of 40% formaldehyde solution, and 1 liter of water; said sensitizing means consisting of about 40 grams ammonium dichromate, one gram of a wetting agent and one liter of water and sufficient ammonium hydroxide to change the solution to a light yellow color, said sensitized emulsion being exposed to the action of an actinic source.

GEORGE W. JORGENSEN. 

